This invention relates to a device for constructing a tubular pile foundation in soft soil fromations brought by deposition of mud, clay, mire, slough, sludge and the like. The deposition may be natural or artificial by wasting industrial sludge. The soft soil has linear compression strength below 1 kg/cm.sup.2 in general. Consequently, before earth fill or any structure is loaded on, it is necessary to stabilize the soft soil formations by substituting with firm soils, forming sand drains or solidifing by hardening agent in order to increase the bearing capacity of them.
Among methods for stabilizing the soft soil formations mentioned above, especially in the case of the soil having high water content, it is effective to agitate, mix it with the chemical hardener slurry and then solidify all the agitated cylindrical portion in situ to make a column pile. The bearing capacity of the column pile thus formed is caused mainly by frictional force at its peripheral surface, provided that it does not have any footing at its lowermost end. In other words, the unimportant central portion is also solidified. As a result of it, the area needed to agitate becomes great and then the greater power is required for driving agitating blades. Moreover a lot of the chemical hardener slurry is also required. In addition to the aforementioned drawbacks, the period of the work is rather long since many column piles are formed to cover a desired area worked upon.